There are various bleeding disorders caused by deficiencies of blood coagulation factors.
The most common disorders are hemophilia A and B, resulting from deficiencies of blood coagulation Factor VIII (FVIII) and IX, respectively. Another known bleeding disorder is von Willebrand's disease (VWD).
In plasma FVIII exists mostly as a noncovalent complex with von Willebrand Factor (VWF), and its coagulant function is to accelerate Factor IXa dependent conversion of Factor X to Xa.
Classic hemophilia or hemophilia A is an inherited bleeding disorder. It results from a chromosome X-linked deficiency of blood coagulation FVIII, and affects almost exclusively males with an incidence of between one and two individuals per 10,000. The X-chromosome defect is transmitted by female carriers who are not themselves hemophiliacs. The clinical manifestation of hemophilia A is an increased bleeding tendency.
In severe hemophilia A patients undergoing prophylactic treatment FVIII has to be administered intravenously (i.v.) about 3 times per week due to the short plasma half-life of FVIII of about 12 to 14 hours. Each i.v. administration is cumbersome, associated with pain and entails the risk of an infection especially as this is mostly done at home by the patients themselves or by the parents of children having been diagnosed for hemophilia A.
It would thus be highly desirable to increase the half-life of FVIII so that pharmaceutical compositions containing such FVIII would have to be administered less frequently.
Several attempts have been made to prolong the half-life of non-activated FVIII either by reducing its interaction with cellular receptors (WO 03/093313 A2, WO 02/060951 A2), by covalently attaching polymers to FVIII (WO 94/15625, WO 97/11957 and U.S. Pat. No. 4,970,300), by encapsulation of FVIII (WO 99/55306), by introduction of novel metal binding sites (WO 97/03193), by covalently attaching the A2 domain to the A3 domain either by peptidic (WO 97/40145 and WO 03/087355) or disulfide linkage (WO 02/103024A2) or by covalently attaching the A1 domain to the A2 domain (WO2006/108590).
Another approach to enhance the functional half-life of FVIII or VWF is by PEGylation of FVIII (WO 2007/126808, WO 2006/053299, WO 2004/075923) or by PEGylation of VWF (WO 2006/071801) The increased half-life of pegylated VWF would indirectly also enhance the half-life of FVIII present in plasma. Also fusion proteins of FVIII have been described (WO 2004/101740, WO2008/077616 and WO 2009/156137).
VWF, which is missing, functionally defect or only available in reduced quantity in different forms of von Willebrand disease (VWD), is a multimeric adhesive glycoprotein present in the plasma of mammals, which has multiple physiological functions. During primary hemostasis VWF acts as a mediator between specific receptors on the platelet surface and components of the extracellular matrix such as collagen. Moreover, VWF serves as a carrier and stabilizing protein for procoagulant FVIII. VWF is synthesized in endothelial cells and megakaryocytes as a 2813 amino acid precursor molecule. The amino acid sequence and the cDNA sequence of wild-type VWF are disclosed in Collins et al. 1987, Proc. Natl. Acad. Sci. USA 84:4393-4397. The precursor polypeptide, pre-pro-VWF, consists of an N-terminal 22-residue signal peptide, followed by a 741-residue pro-peptide and the 2050-residue polypeptide found in mature plasma VWF (Fischer et al., FEBS Lett. 351: 345-348, 1994). After cleavage of the signal peptide in the endoplasmatic reticulum a C-terminal disulfide bridge is formed between two monomers of VWF. During further transport through the secretory pathway 12 N-linked and 10 O-linked carbohydrate side chains are added. More important, VWF dimers are multimerized via N-terminal disulfide bridges and the propeptide of 741 amino acids length is cleaved off by the enzyme PACE/furin in the late Golgi apparatus.
Once secreted into plasma the protease ADAMTS13 can cleave high-molecular weight VWF multimers within the A1 domain of VWF. Plasma VWF therefore consists of a whole range of multimers ranging from single dimers of 500 kDa to multimers consisting of up to more than 20 dimers of a molecular weight of over 10,000 kDa. The VWF-HMWM hereby having the strongest hemostatic activity, which can be measured in ristocetin cofactor activity (VWF:RCo). The higher the ratio of VWF:RCo/VWF antigen, the higher the relative amount of high molecular weight multimers.
In plasma FVIII binds with high affinity to VWF, which protects it from premature elimination and thus, plays in addition to its role in primary hemostasis a crucial role to stabilize FVIII, regulate plasma levels of FVIII and as a consequence is also a central factor to control secondary hemostasis. The half-life of non-activated FVIII bound to VWF is about 12 to 14 hours in plasma. In von Willebrand disease type 3, where no or almost no VWF is present, the half-life of FVIII is only about 2 to 6 hours, leading to symptoms of mild to moderate hemophilia A in such patients due to decreased concentrations of FVIII. The stabilizing effect of VWF on FVIII has also been used to aid recombinant expression of FVIII in CHO cells (Kaufman et al. 1989, Mol Cell Biol 9:1233-1242).
VWF-derived polypeptides, in particular VWF fragments, have been described to stabilize FVIII in vitro and in vivo. WO 2013/106787 A1 is directed at chimeric proteins comprising certain VWF fragments and a FVIII protein. Those chimeric hetero-dimers of FVIII and VWF-fragment do have a fixed molar ratio of VWF to FVIII of 1:1. WO 2014/198699 A2 and WO 2013/083858 A2 describe VWF fragments and their use in the treatment of hemophilia. It was found that bioavailability of FVIIIs may be significantly improved upon extravascular co-administration with similar molar amounts of VWF fragments. High molar excess of VWF over FVIII was said to be not desirable, and in experiments with VWF fragments co-administered s.c. with FVIII it was found that the VWF dose was not critical for FVIII bioavailability. Thus molar ratios of VWF fragments over FVIII were limited to maximally 50:1 and preferred ranges to maximally 1.5:1. WO 2011/060242 A2 discloses fusion polypeptides comprising certain VWF fragments and an antibody Fc region proposing specific molar ratios of VWF fragment over FVIII of up to 10:1. WO2013/093760 A2 describes a method for preparing a protein, comprising co-expressing FVIII or VWF polypeptides, including truncated forms of VWF, with a recombinant α-2,3-sialyltransferase. Yee et al. (2014) Blood 124(3):445-452 found that a VWF fragment containing the D′D3 domains is sufficient to stabilize Factor VIII in VWF-deficient mice. However, although a VWF D′D3-Fc fusion protein exhibited markedly prolonged survival when transfused into FVIII-deficient mice, the VWF D′D3-Fc fusion protein did not prolong the survival of co-transfused FVIII. The prior art is silent as to the benefit of exceeding certain ratios of administered VWF fragments over endogenous VWF for the purpose of prolonging the in vivo half-life of co-administered FVIII.
There is an ongoing need for methods increasing the half-life of FVIII and FVIII products with reduced administration frequency.